Tool alloy



United States Patent Office 3,249,428 Patented May 3, 19.66

3,249,428 TOOL ALLOY Sidney Weisman, West Caldwell, N.J., assignor to Howe Sound Company, acorp'oration offNew Jersey No Drawing. Filed Nov. 14, 19 63, Ser, No. 323,609

3 (Elaims. (Cl. 75171) This invention relates to a tool alloy, of the type containing about 40 to 60% by weight cobalt and 25 to 35% by weight chromium, along with small amounts of carbon, silicon, manganese and nickel. More particularly, it relates to an alloy of this type which is improved by the addition of relatively high amounts of molybdenum and tungsten and not more than a small percentage of iron.

The tool alloy composition of the invention is particularly designed for use in the manufacture of surgical tools and various cutting tools. The fundamental properties of all tool alloys are that they must possess good wear resistance, toughness, and hardness. In addition alloys which are to be used as cutting tools must have high resistance to abrasion and good edge retention characteristics. Another essential property, if the alloy composition is to be used for the manufacture of cutting tools having surgical applications, is resistance to corrosion. Of the nonferrous alloys which are used in the manufacture of tool alloys, those found to be most successful are usually classified on the basis of their alloy content such as cobalt-chromiumtungsten, or cobalt-chromium-nickel-tungsten with molybdenum replacing all or part of the tungsten. The alloy of the invention constitutes an improvement over these known cobalt alloys in that it has been found to have increased hardness and strength and superior edge retention properties.

Broadly stated, the alloy of the invention constitutes an improvement in tool alloys which contain about 40 to 60% by weight cobalt, 25 to 35% by weight chromium and small amounts of carbon, silicon, manganese and nickel. The improvement in the alloy of the invention comprises the addition of 3 to 4% by weight molybdenum, 8.5 to 11% by weight tungsten and not more than about 1% iron. The main characteristic of this new alloy is that it contains relatively high tungsten content plus a relatively high molybdenum content which has in testing been shown to provide greater hardness and strength during its use and excellent edge retention characteristics which are so important in the manufacture of files, rasps, reamers, cutters, drills, and other types of cutting tools especially those which have surgical uses.

More specifically stated the tool alloy of the invention can have the following composition in the given range in percentages by weight: chromium 25 to 35%; tungsten 8.5 to 11%; molybdenum 3 to 4%; nickel 2 to 3%; manganese 1 to 3%; carbon 1 to 2%; iron 1% max.; silicon 2% max; and the balance cobalt.

Set forth below in Table I is the preferred range of the alloy composition along with the nominal composition in a preferred range, and the specific composition of one sample which has been tested.

In testing the alloy composition of the invention it was found that the composition was easily castable into intricately shaped tools, and the tools showed a high cast hardness of approximately Rockwell C 46 to 49. In one example a sample was cast into a bone reamer which operated excellently and'repeatedly without need-of regrinding. In all cases thetools madewith the new alloyprovedtohave good abrasionresistance and goodedge retention characteristics. Furthermore, the alloy had good grindability which permitted developing the necessary clearances and cutting edges of the particular tool. Finally it was found that repeated autoclaving did not rust the new alloy composition thereby indicating the high corrosion resistance which it possessed.

The new alloy composition was comparatively tested with well-known cobalt alloy compositions set forth in Table II as alloy A and alloy B.

'TABLE II Composition A Composition B The comparative tests were carried out by casting reamer implements; In practice alloy A was found to be too soft in the cast or wrought condition for satisfactory cutting of the bores. Alloy B was found not to possess the required strength and edge retention which are so essential in this type work. The alloy of the invention, however, performed very satisfactorily under similar tests and similar conditions and was found to have excellent combination of properties which permitted the tool to be used successfully in all the reamer applications.

It is theorized that the results with the new alloy composition are achieved by the relatively high molybdenum content which combined with the tungsten, chromium, nickel, carbon, manganese and cobalt provide the unique properties of good abrasion resistance, toughness, cutting edge sharpness retention-and hardness. The novel combinations of the molybdenum and tungsten in the percentages recited above plus the low iron impurity content which is closely controlled in the alloy composition, combine to .give these advantageous characteristics.

I claim:

1. A tool alloy consisting essentially of the following in percent by weight:

W 9.0 to 10.5 Mo 3.4 to 3.8 N1 2.25 to 2.75 Mn 1.80 to 2.20 C 1.20 to 1.40

Fe, max. 1 Si 0.5 to 1 Co Balance 2. A tool alloy consisting essentially of the following in nominal percentages by weight:

4 References Cited by the Examiner UNITED STATES PATENTS 2,309,371 1/1943 Wissler 75-171 3,068,096 12/1962 Elbaum et a1 75171 FOREIGN PATENTS 219,293 5/1929 Great Britain. 778,359 7/1957 Great Britain.

DAVID L. RECK, Primary Examiner. WINSTON A. DOUGLAS, Examiner. C. M. SCHUTZMAN, R. O. DEAN, Assistant Examiners. 

1. A TOOL ALLOY CONSISTING ESSENTIALLY OF THE FOLLOWING IN PERCENT BY WEIGHT: 